From: Rik van Riel <riel@conectiva.com.br> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-hackers@FreeBSD.ORG, <freebsd-net@FreeBSD.ORG> Subject: Re: Another go at bandwidth delay product pipeline limiting for TCP Message-ID: <Pine.LNX.4.44L.0207200005190.12241-100000@imladris.surriel.com> In-Reply-To: <200207200245.g6K2jHOh081549@apollo.backplane.com>
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On Fri, 19 Jul 2002, Matthew Dillon wrote: > :It's not too hard actually. Random early drop should be > :enough for incoming packets, just artificially restrict > :the bandwidth to something like 90% of your maximum > :download bandwidth and drop packets that come in too > :fast. > : > :This will cause tcp to slow down to the speed limit you've > :chosen and the ISP queue will never fill up. > > As a receive side mechanism the idea has merit, but I really > dislike artificallly dropping packets as a means of controlling > TCP. It's impossible to know what the effect of the drop would > have on the remote host's protocol stack. I agree it's pretty crude, but it seems to work wonders on my DSL line. I'm using a slightly changed version of the wondershaper script (for Linux)... > Your comment on limiting the bandwidth to 90% of maximum is > really humerous to me! I spent good two hours trying to get > the sender-side algorithm to maintain >90% maximum available > bandwidth. The algorithm I am using winds up being the most stable > at around 88% and it took a bit of messing around to get it > to stabilize at > 90%. I expect a receiver side algorithm would > have the same problem. Absolutely. On my DSL things work best when I limit myself to 220 kbit/s down (from the maximum 256 kbit/s), or about 85% of the bandwidth. For sending I'm using cbq as the top scheduler, dividing traffic in the categories 'interactive', 'bulk' and 'traffic we hate', each of these has a token bucket filter (tbf) leaf scheduler to keep latencies down. Sending is also limited to about 85% of the bandwidth. OTOH, the DSL hardware here seems to be a bit broken, fast uploads seem to interfere with the download and break the download speed. I can run one-way traffic with low latency all the way up to about 95% of the bandwidth... regards, Rik -- Bravely reimplemented by the knights who say "NIH". http://www.surriel.com/ http://distro.conectiva.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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